1. Field of the Invention
The present invention relates to an ultrasound diagnostic apparatus and ultrasound image processing program which actively extract and display microstructures in living organs and the like from echo signals from tissue.
2. Description of the Related Art
Ultrasound diagnosis makes it possible to display how the heart beats or the embryo moves in real time by simple operation of tapping an ultrasound probe on the body surface, and allows repetitive examination because it is highly safe. In addition, the system size is smaller than other diagnostic equipment such as X-ray, CT, and MRI equipment, and hence the apparatus can be moved to a bed side to allow easy examination. Ultrasound diagnostic apparatuses vary depending on the types of functions which they have. For example, an ultrasound diagnostic apparatus having a size that allows an operator to carry it with his/her one hand has been developed, and ultrasound diagnosis is free from the influence of radiation exposure such as X-ray exposure. Therefore, this apparatus can be used in obstetrical treatment, treatment at home, and the like.
Such types of ultrasound diagnosis include breast cancer early diagnosis. It is known that in many cases, micro calcification occurs in breast tissue as a symptom of breast cancer. One or a few calcified lesions are scattered in local portions. Lime is harder than living tissue, and hence reflects well ultrasound waves. Therefore, such a calcified lesion is expected to exhibit high brightness on an image. It is, however, difficult to extract such a lesion in an image by visual recognition even if it has a size of about several hundred μm.
In some cases, interference fringes called speckle patterns due to random interference between ultrasound waves are produced on an ultrasound image. On the other hand, this pattern is very similar to a microstructure such as a micro calcified substance which tends to be overlooked in, for example, the above breast cancer diagnosis, and hence sometimes becomes misleading image information. For this reason, in the above breast cancer diagnosis or the like which requires no speckle pattern, in order to remove the pattern, for example, the following processing is performed: spatial compounding (see, for example, patent references 1, 2, 3, and 4), CFAR (Contrast False Alarm Rate) processing, similarity filter processing and other speckle reduction processes, MIP (Maximum Intensity Projection) processing, and image condition adjustment. Note that these techniques are disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication Nos. 61-189476, 2001-238884, 2003-61964, and 2004-321582. Although not included in the ultrasound field, various attempts to automatically recognize micro calcification have been reported mainly as applications of X-ray diagnostic images, as disclosed in, for example, U.S. Pat. No. 3,596,792.
However, for example, the following problems arise in the above conventional techniques for properly observing microstructures by removing speckle patterns.
In speckle reduction using CFAR processing, although the contrast ratio of a microstructure can be relatively increased, in a case wherein a living body is three-dimensionally scanned to search for a minute substance, oversight still occurs. Even if, for example, a microstructure is displayed in a given frame, the time required to move a scan slice is generally shorter than the time required to find (acknowledge) the microstructure.
MIP processing is suitable for the observation of an approximate shape of an organ. If, however, a speckle pattern and a microstructure are superimposed on each other, the contrast ratio of a minute substance decreases. Therefore, an image having undergone MIP processing alone is not sufficient for the observation of a microstructure.
In addition, in image quality condition adjustment, e.g. dynamic range or gain, if the operator manually makes adjustments, an image which is suitable to some extent can be obtained. If, however, the operator makes wrong settings, a microstructure may not be displayed or speckles may remain. In addition, since optimal set values vary depending on the state of a subject (attenuation due to subcutaneous fat), it is no use to record optimal values. Furthermore, the image based on the above set values does not often allow the operator to see an approximate shape of an organ in the prior art. With this image alone, therefore, it may sometimes become difficult to specify a slice.